1. Field of Use
These teachings relate generally to a system and method for inductively coupling power to electric vehicles and more particularly to an apparatus and method for inductively coupling power through the tires, rim, or wheel of an electric, vehicle.
2. Description of Prior Art (Background)
Electric powered transportation is generally more efficient and less polluting than petroleum powered vehicles. Vehicles traveling on fixed routes such as subways, streetcars, and railroad trains often use electric motive power due to its efficiencies. These vehicles might use a catenary wire, overhead wire, or third rail system to transmit power to the vehicle.
The capability to transmit electricity to vehicles enables electric vehicles to have nearly unlimited range without having to recharge onboard batteries or refuel with liquid hydrocarbons, e.g., gasoline for comparatively inefficient, internal combustion engines. For example, the average efficiency of an internal combustion engine in conversion of gasoline to motion is about 12-15% whereas electric vehicles convert, about 80-90% of electric power to motion.
The primary limitation for electric vehicles such as cars and trucks has been the storage or transmission of electricity onboard the vehicle. For example, lithium batteries typically used for powering electric vehicles contain 100 WH/kg and take hours to recharge.
The primary solutions currently being proposed for electric vehicle transportation are better batteries and faster charging, battery swapping systems, and plug-in hybrid vehicles. Each one has their limitations and will not solve the problem of electric vehicle transportation in the long run.
Batteries and fast charging: in general, the time for charging lithium-ion batteries is unacceptable for mainstream usage. Even if lithium-ion batteries could be theoretically recharged in 5 minutes, the infrastructure needed to transmit the tremendous currents needed for fast charging, on the order of 2000 Amps for each vehicle, is unrealistic and not feasible.
Battery Swapping: Battery swapping could theoretically solve the problem of fast energy replacement in electric vehicles, but the standardization required has no precedent (consider electric hand tools), the logistics are unwieldy, and it was explored during the 1990's unsuccessfully. It also fails the criteria of being a superior system to current technology.
Plug-in hybrid Vehicles: Plug-in hybrid vehicles run primarily by electric, power, with internal combustion back-up combining the best features of both. In the short term they dramatically increase the efficiency of vehicles by running mainly on electric power, and using internal combustion power as a backup or secondary power source. Hybrid vehicles may serve as a transitional vehicle to a pure electric vehicle future. But in the long run they fail the criteria of avoiding petroleum. Even using bio-fuel they still use the inefficient internal combustion engine.
Other prior art solutions to powering electric vehicles include inductively coupling power from an electrified roadway across an air gap to the electric vehicle. However, it will be appreciated that the feasibility of transmitting power to vehicles through induction using wires buried in the roadway has been proven indoors and in warm, sunny climates such as California and Florida where an inductive pickup is positioned such that the maximum air gap is 10 cm.
However, the problem of an inductive, pick-up hanging under the car close to the road in snow and ice is a previously unsolved problem. It will be appreciated that such an arrangement is unsuitable for any less-than-ideal road conditions since the pick-up would be subject to road debris, snow and ice during, had weather.
More recent prior solutions have placed the secondary pick-up at a greater distance from the road, such as 5 inches, to avoid contact with debris. The greater air gap has the disadvantage of lower transmission efficiency.